Maintenance optimization

My name is Gabrijela Obradović and I am a PhD student in Mathematical Optimization at Chalmers University of Technology. I hold a Master’s degree in Applied Mathematics from University of Novi Sad and I did my master thesis at Descartes University in Paris, which together led to the ECMI Postgraduate Programme Mathematics in Industry certificate. Since Fall 2018, I have been working on an industrial project with the aerospace and defence company Saab. My main supervisor is prof. Ann-Brith Strömberg and our industrial connection is Kristian Lundberg (Saab). The project is funded by the Swedish Governmental Agency for Innovation Systems (VINNOVA; project number 2017-04879), Chalmers University of Technology and Saab.

Maintenance optimization means deciding which maintenance activities to perform, and when, such that one or several objectives are optimized. Performing maintenance operations in a good fashion is of big importance. Maintenance budgets on average represent a significant portion of the total plant operating budget, varying from a few percent in lighter manufacturing to a high percentage in equipment-intensive industries. Moreover, hidden costs are usually not accounted for. Ineffective maintenance management policies often lead to a big increase in costs and most importantly, a decrease in efficiency.

My research is focused on mathematical modeling, optimization and scheduling of maintenance of aircraft components and of the maintenance workshop, where components are sent for repair. While an aircraft operates, its components deteriorate and in order for it to remain operational, (preventive and/or corrective) maintenance of its components is required. Components that are to be maintained are sent to the maintenance workshop, which needs to schedule and perform all maintenance activities while satisfying the contract. Our modelling is based on a mixed-binary linear optimization model of a preventive maintenance scheduling problem with so-called interval costs over a finite and discretized time horizon. We extend this scheduling model with the flow of components through the repair workshop, including stocks of spare components, damaged and repaired ones. Along with the scheduling problem, we address and analyze two different contracting forms between the two respective stakeholders: the aircraft operator and the maintenance workshop. Namely, an availability of repaired components contract and a repair turn-around-time contract of components sent to the maintenance workshop.

One of the possible extensions, which is important for the intended application of this work, would be to introduce corrective maintenance (i.e. maintenance action once an unexpected failure occurs). At the current stage, the means to handle unexpected failures are to reduce the risk for such failures by not allowing too large maintenance intervals and reschedule the maintenance plan whenever an unexpected event occurs. Since short-term changes in the operational schedules, as well as in the schedules for the maintenance workshop, are often inconvenient and sometimes not even feasible, (if possible) the rescheduling should be such that the solution remains fixed for a certain number of time steps.

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